Postsynthesis of mesoporous MOR-type titanosilicate and its unique catalytic properties in liquid-phase oxidations

Mesoporous titanosilicate with the MOR topology, denoted as Ti-Meso-MOR, was postsynthesized from commercially available mordenite by sequential acid, alkaline, acid, and TiCl₄ vapor treatments, and its catalytic oxidation properties were investigated in detail in liquid-phase oxidation reactions with hydrogen peroxide as an oxidant. A controllable acid leaching was first carried out on H-mordenite (Si/Al = 7.8) to induce a partial dealumination to Si/Al = 80, which was suitable for constructing secondary mesopores by subsequent alkaline treatment. Alkaline treatment-induced desilication introduced a large number of intracrystal mesopores. Tetracoordinated Ti species were then inserted into the resultant mesoporous mordenite with a high dealumination degree (Si/Al = 145) through the gas-solid reaction with TiCl₄ vapor at elevated temperatures. In comparison with conventional Ti-MOR and TS-1, Ti-Meso-MOR thus prepared exhibited an improved catalytic activity in the hydroxylation of toluene and the ammoximation of cyclohexanone as well. Moreover, Ti-Meso-MOR proved to be a robust catalyst for continuous ammoximation since the mesopores minimized diffusion limitation and suppressed coke formation efficiently.